The construction of dropped ceilings usually involves the use of a grid of so-called ceiling tees, which are hung below a structural portion of the building usually on wires or rods. Ceiling tiles are laid in the majority of the grid, and at various locations other fixtures such as air handling fixtures, and lighting fixtures are inserted.
In other forms of dropped ceilings, some other form of finishing surface may be provided in some cases, with suitable openings being located at spaced apart points for reception of lighting fixtures.
The installation of such lighting fixtures is usually done from beneath the ceiling. The lighting fixture is raised upwardly and presented to the ceiling at the appropriate opening. It must then be tilted at an angle, and inserted upwardly through the opening, and then lowered back in a horizontal fashion, so that it rests on the supporting fabric of the ceiling.
At the same time, access must be had to the space above the ceiling, so that suitable electrical connections can be made to wiring harnesses and the like which are located in the space above the ceiling.
In some cases, air handling slits or openings are provided around such lighting fixtures, and in some cases it is also necessary to attach air handling duct work and the like to such slits.
The most popular size of lighting fixture employed in such ceilings is a fixture which measures 2 ft. by 4 ft., and fits in the typical grid of ceiling tees. However in other ceiling designs, lighting fixtures may be employed which are 2.times.2 or 4.times.4, or may be of a custom design shape, depending upon the specifications of the architects and consulting engineers involved. In the past, the weight of the lighting fixtures has been considerable, and consequently the work involved in installing and positioning the lighting fixtures in the ceiling openings is relatively speaking exhausting, and usually requires two men per fixture. One of the principal limiting factors in the design of such lighting fixtures is of course that they must meet severe product specifications laid down by various authorities such as the Underwriters' Laboratory and national standards associations in various countries. These standards are imposed both to provide electrical safety in the system in the event of failure of a component such as a ballast, insulation or the like, and also to provide resistance to fire, and heat developed by the lighting elements.
In order to meet these specifications, it is necessary to employ relatively heavy gauge metal in the construction of such lighting fixtures, and this greatly adds to the weight and also to the expense of the lighting fixtures themselves.
Another factor is the degree and intensity of lighting which is to be provided in a particular building space. The type of work carried on in a building space, the height of the ceiling above the work area, and the degree of available natural light and the like are all factors which must be taken into account. However, there are certain minimum standards which are generally accepted in the industry for the design of typically commercial buildings such as office spaces, showrooms and the like, which require a relatively high degree of lighting intensity.
In order to provide this degree of lighting intensity it is necessary to provide lighting elements at relatively frequent intervals throughout the ceiling, and also to provide lighting elements having a fairly high degree of lighting intensity.
The provision of such relatively high intensity lighting carries with it additional problems. It is found from experience and numerous tests that the use of relatively high intensity lighting in such ceilings creates stresses on the persons working in the work area. Efforts have been made in the past by the provision of various designs of lenses and the like to ensure that the intensity of the lighting is directed to the area beneath the light fixture itself. Areas displaced more than a certain angular distance away from the lighting fixture are generally speaking subject to a reduced intensity lighting. The object of this is to ensure that persons walking about the space or looking about from one area to another, will not find that their eyes are constantly receiving high intensity lighting at a relatively low angle from more distant lighting fixtures.
However, the various expedients used to provide this desirable characteristic, which may be characterized simply as the reduction of low angle incident light, have not generally speaking been totally satisfactory.
One expedient that has been particularly successful is to locate the lighting elements in upwardly recessed areas in the ceiling known as "coffers." The provision of such upwardly recessed coffers provides a simple solution to the problem of low angle glare. Since the tubes themselves are located in the upwardly directed recesses, all light from the tubes beyond a certain predetermined angle, is simply cut off altogether. In practice it is found that the use of a coffered ceiling system greatly increases the aesthetic appeal of the ceiling, and also adds somewhat to the variety of the surface appearance, and reduces stresses on persons working the building space.
However, coffered ceilings have been found to be relatively expensive to construct. In particular, they are found to be unusually labour intensive, and consequently have not found wide acceptance.
An additional factor in the design of such lighting fixtures is the transportation of such fixtures from the factory to the work site. The coffered ceiling lighting fixtures such as have been available in the past, have a relatively considerable height dimension. Since most of this dimension consists of empty space, it is readily apparent that the shipping of such coffered lighting fixtures is relatively inefficient and therefore expensive.
It is therefore clearly desirable to provide an improved form of lighting fixture which both provides for a recessed or coffered ceiling effect, and which at the same time can be fabricated at least in part of more economical thin gauge sheet metal, and which also provides for a partially knocked down form of construction, such that it may be shipped in such a manner that it occupies less space than when it is set up.